[media] media: mx2-emmaprp: Add missing mutex_destroy()

This patch adds the missing mutex_destroy(), when the driver is removed.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>